The Rock Mass Rating (RMR) System was introduced over 40 years ago, and since then has become a worldwide reference, along with the Q system, for design applications involving estimation of rock mass properties and tunnel support. A massive database of experience has been recorded in the process. On the 25th anniversary of the last modification of the RMR System in 1989, known as the RMR89, an update of this index has now been performed to incorporate the innovations introduced in recent decades and to improve its performance. For this purpose a database of 2,298 cases of RMR89’s was compiled from tunnel faces. Based on the experience gained in the last decades, a new RMR14 has been developed, which has a new structure comprising five basic parameters and three adjustment factors. Also a clear correlation between RMR89 and RMR14 is provided and shows that the essence of the RMR System has been maintained for practical use.